Select, weight, and mix the colors you want, we used PP shredded bottle caps.

Fill the injection machine and wait for the plastic to start flowing, with a small nozzle and a constant weight applied on the machine, use a wooden rod to "screw" the filament around it, make it as long as you want, we recommend using a wooden rod because the plastics sort of sticks and makes it easier to form the spring.

Remove the small nozzle from the injection machine and extrude some plastic on a flat sheet, press it against another sheet in a press, wait for it to cool and remove the plastic sheet, cut it to shape, make the holes and assemble the notebook.

Try different combinations, you can make the springs out of the same mixture of however you want :)